1. Field of the Invention
This invention broadly relates to appliances that are used during the course of orthodontic treatment. More particularly, the present invention relates to orthodontic appliances that are provided with built-in torque as well as a latch for releasably retaining an archwire in an archwire slot of the appliance.
2. Description of the Related Art
Orthodontic therapy is a specialized type of treatment within the field of dentistry, and involves movement of malpositioned teeth to improved locations along the dental arches. Orthodontic treatment often enhances the patient's facial appearance, especially in regions near the front of the oral cavity. Orthodontic treatment can also improve the patient's occlusion so that the teeth function better with each other during mastication.
Many types of orthodontic treatment programs involve the use of a set of tiny appliances and archwires that are commonly known collectively as “braces”. During such treatment programs, small appliances known as brackets are fixed to the patient's anterior, cuspid and bicuspid teeth, and an archwire is inserted into a slot of each bracket. The archwire forms a track to guide movement of the teeth to orthodontically correct locations. End sections of the archwires are often captured in tiny appliances known as buccal tubes that are fixed to the patient's molar teeth.
Many orthodontic brackets have small wings known as “tiewings” that are connected to a body of the bracket. Once the bracket has been attached to a tooth and an archwire has been placed in the archwire slot of the bracket, a ligature is coupled to the bracket in order to retain the archwire in the archwire slot. One common type of commercially available orthodontic ligatures is a small, elastomeric O-ring that is installed by stretching the O-ring along a path behind the tiewings and over the facial side of the archwire.
Certain types of orthodontic brackets are known as self-ligating brackets, and are provided with a latch for coupling the archwire to the bracket. Use of the latch avoids the need to use a ligature to couple the archwire to the bracket. The latch may comprise a movable clip, spring member, cover, shutter, bale or other structure that is connected to the bracket body for retaining the archwire in the archwire slot.
Improved, self-ligating orthodontic brackets are described in applicant's published PCT applications entitled “ORTHODONTIC APPLIANCE WITH SELF-RELEASING LATCH”, Nos. WO01/22901 and WO02/089693. The appliances described in those applications have a latch for retaining an archwire in the archwire slot, and the latch releases the archwire from the archwire slot whenever the archwire exerts a force on the appliance that exceeds a certain minimum value. The minimum value is significantly less than the force required in the same direction to debond the appliance from the tooth, and consequently helps ensure that the appliance will not spontaneously debond from the tooth during the course of treatment.
Many orthodontic appliances have an archwire slot that has a rectangular cross-sectional configuration when viewed in reference planes perpendicular to the longitudinal axis of the archwire slot. When an archwire having a matching rectangular cross-sectional configuration is placed in the archwire slot, the sides of the archwire can exert in certain situations a pivotal force on the appliance in directions along an arc about the longitudinal axis of the archwire. This pivotal force is commonly referred to as “torque” and serves to pivot the associated tooth in a corresponding direction as may be desired. For example, the practitioner may exert torque on a somewhat inclined upper front tooth in order to move the tooth toward a more upright orientation.
One common orthodontic treatment technique is known as the “straight wire technique”. In this technique, brackets and buccal tubes are selected and placed at certain locations on the teeth so that the curved archwire is level and extends in a flat reference plane at the conclusion of treatment. Use of the straight wire technique often obviates the need for the practitioner to place bends or twists in the archwire, resulting in a savings of time for both the practitioner and the patient.
Certain orthodontic appliances with rectangular archwire slots are provided with “built-in torque” or “pre-applied torque”. In those appliances, the sides of the archwire slots are oriented at a certain angle with respect to the base of the appliance. The angle is selected according to the desired angular orientation of the tooth at the end of treatment such that the top and bottom sides of the archwire slot lie in corresponding reference planes that also contain the top and bottom sides of archwire slots of other appliances in the same dental arch. As a result, the practitioner using the straight wire technique need not place a twist in the archwire in order to move the adjacent tooth to its desired angular inclination.
Self-ligating orthodontic appliances having a latch with one or more clips such as the clips described in the PCT applications mentioned above may be provided with built-in torque as described in the preceding paragraphs. It is desirable for such pre-torqued, self-ligating appliances to be as small as possible in order to minimize patient discomfort and undue contact with oral tissue. However, it is also important to ensure that the latch reliably opens and closes as intended over extended periods of time and does not fracture during use.